The present invention relates to an optical pickup device for use in an optical disk apparatus for recording and reproducing data at high density.
It is required that the optical disk apparatus be compact, light and low in cost. To satisfy the requirements, various integrated optical units are proposed. An integrated optical unit constitutes an optical pickup device in combination with an objective optical system for converging a light beam on an optical disk, and if necessary, a collimate lens. An integrated optical unit includes a number of components necessary for an optical pickup device, for example, a semiconductor laser, a photodiode, a prism for splitting an optical path, and a hologram element. These components are contained in a single package.
The optical disk apparatus is also required to operate at a high speed. The high speed operation is generally achieved by increasing the rotation speed of the optical disk, thereby increasing the data transfer rate. Writing of data at a high rotation speed requires high laser power. However, since a semiconductor laser used as a light source has a limited output, the optical pickup device is required to have low optical loss and high coupling efficiency.
A light beam emitted from a semiconductor laser generally has elliptic distribution of quantity of light. For this reason, an optical pickup device that converges a light beam without changing the distribution of quantity of light has low coupling efficiency, since part of the elliptic distribution along the major axis is not utilized. To improve the coupling efficiency, a preferable optical pickup device includes a beam converting system for converting a light beam having elliptic distribution of quantity of light generally emitted from the semiconductor laser to a light beam having circular distribution of quantity of light. The use of such a beam converting optical system is indispensable for an optical disk apparatus particularly for recording and reproducing data at high density.
As described above, the conventional optical pickup device produces some results from an aspect of reduction in size, weight and cost of the optical disk apparatus, through the use of an integrated optical unit, and from an aspect of increase in operation speed of the optical disk apparatus through the use of a beam converting optical system.
However, demands for reduction in size, weight and cost and increase in operation speed of the optical disk apparatus will continuously increase. Therefore, it is requested that a further improved optical pickup device advantageous in these aspects be provided.
An object of the present invention is to provide an optical pickup device further improved in aspects of reduction in size, weight and cost and increase in operation speed of an optical apparatus, and particularly an optical pickup device having an improved beam converting optical system.
Another object of the present invention is to provide an optical pickup device having a beam converting optical system adapted to be combined with an integrated optical unit.
A still another object of the present invention is to provide an optical pickup device having a beam converting optical system which contributes to improvement of the S/N ratio of an optical disk apparatus.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.